This is where I've gone for refills:
http://www.vetmeddeals.com/animal-be...-c-70_102.html

they come out to $14.99 each. I also bought a bunch of the plug in diffusers off of ebay (no bottles included). A while back I got 5 of them for $5.00 total! Check out ebay as well for that.

I can't get on the other website that was first mentioned.